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1 – 10 of 578Ferdinand Schmid, Constantin Paschold, Thomas Lohner and Karsten Stahl
Internal gearings are commonly used in transmissions due to their advantages like high-power density. To ensure high efficiency, load-carrying capacity and good noise behavior, a…
Abstract
Purpose
Internal gearings are commonly used in transmissions due to their advantages like high-power density. To ensure high efficiency, load-carrying capacity and good noise behavior, a profound knowledge of the local gear mesh is essential. The tooth contact of internal gears relates to a convex and concave surface that form a conformal contact. This is in contrast to external gears, where two convex surfaces form a contraformal contact. This paper aims at a better understanding of conformal contacts under elastohydrodynamic lubrication (EHL) to improve the design of internal gearings.
Design/methodology/approach
An existing numerical EHL model is used for studying the characteristic properties of a hard conformal EHL line contact. A hard contraformal EHL line contact is studied as reference. Non-Newtonian fluid behavior and thermal effects are considered. By taking into account the local contact conformity and kinematics, the effects and relevance of the curvature of the lubricant gap and micro-slip are analyzed. In a parameter study, scale effects of the contact radii on film thickness, temperature rise and friction are examined.
Findings
The curvature of the lubricant gap and effects of micro-slip are small in hard conformal EHL line contacts. For high micro-slip, it can be neglected. Hence, the modeling of conformal contacts using an equivalent geometry of the contact problem is reasonable. The parameter study shows beneficial tribological aspects of the conformal contact compared to the contraformal contact. Higher film thickness and lower fluid coefficient of friction are observed for conformal contacts, which can be attributed to lower pressures for the case of the same external normal force, or to a higher contact temperature rise for the case of equivalent contact pressure.
Originality/value
Despite its widespread existence, the local geometry and kinematics in hard conformal EHL line contacts like in internal gearings have been rarely studied. The findings help for a better understanding of local contact characteristics and its relevance. The quantified scale effects help to improve the efficiency and load-carrying capacity of machine elements with hard conformal EHL contacts, like internal gearings.
Peer review
The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-12-2022-0366/
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Amir R. Khoei, R. Yasbolaghi and S.O.R. Biabanaki
In this paper, the polygonal-FEM technique is presented in modeling large deformation – large sliding contact on non-conformal meshes. The purpose of this paper is to present a…
Abstract
Purpose
In this paper, the polygonal-FEM technique is presented in modeling large deformation – large sliding contact on non-conformal meshes. The purpose of this paper is to present a new technique in modeling arbitrary interfaces and discontinuities for non-linear contact problems by capturing discontinuous deformations in elements cut by the contact surface in uniform non-conformal meshes.
Design/methodology/approach
The geometry of contact surface is used to produce various polygonal elements at the intersection of the interface with the regular FE mesh, in which the extra degrees-of-freedom are defined along the interface. The contact constraints are imposed between polygonal elements produced along the contact surface through the node-to-surface contact algorithm.
Findings
Numerical convergence analysis is carried out to study the convergence rate for various polygonal interpolation functions, including the Wachspress interpolation functions, the metric shape functions, the natural neighbor-based shape functions, and the mean value shape functions. Finally, numerical examples are solved to demonstrate the efficiency of proposed technique in modeling contact problems in large deformations.
Originality/value
A new technique is presented based on the polygonal-FEM technique in modeling arbitrary interfaces and discontinuities for non-linear contact problems by capturing discontinuous deformations in elements cut by the contact surface in uniform non-conformal meshes.
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Dong Guan, Li Jing, Junjie Gong, Zhengwei Yang and Hui Shen
Rotary disc is a key component in the compact spherical pump, connecting shaft and piston, bearing hydraulic force conformally and constituting dynamic working chambers…
Abstract
Purpose
Rotary disc is a key component in the compact spherical pump, connecting shaft and piston, bearing hydraulic force conformally and constituting dynamic working chambers alternatively. Motion of rotary disc comprises two components. One is rotating around its own axis and the other is sliding on a cone surface. Therefore, it is necessary to investigate the friction and wear mechanism between rotary disc and cylinder under a complicated operation condition.
Design/methodology/approach
Structural properties of rotary disc are analyzed first. Frictional moment of rotary disc is modeled based on its structural characteristics and working mechanism, and the constraints of the structural parameters are considered. Besides, the concept of dimensionless contact area is proposed. Comparison is performed between the proposed concept and the frictional moment to determine an optimized beginning angle for spherical pump with a given displacement. The wear model of rotary disc is also established based on its kinematic property, a velocity coefficient is proposed and its common values are presented.
Findings
Effects of structural parameters, i.e. beginning angle and ending angle on the frictional moment, are obtained quantitatively. The frictional moment increases with beginning and ending angle with different rates. While the dimensionless contact area decreases with beginning angle. The larger the piston angle, the larger the velocity coefficient will be. The rotary disc wears severely with a larger beginning angle and smaller ending angle, while it has the smallest wear rate under a smaller beginning angle and a larger ending angle.
Originality/value
The originality lies in modeling the complex contact force of rotary disc based on its specific structure. These conclusions can be used to optimize the structural parameters of rotary disc.
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Because of the specific structure and working mechanism, piston speed is only half of its shaft, which causes severally friction between piston and cylinder. Therefore, the main…
Abstract
Purpose
Because of the specific structure and working mechanism, piston speed is only half of its shaft, which causes severally friction between piston and cylinder. Therefore, the main purpose of this paper is to investigate the friction and wear characteristics of the incomplete spherical piston in spherical pump comprehensively. Finally, to search the low-friction and wear-resistance structural pattern of the piston, and enhance the durability of spherical pump.
Design/methodology/approach
The non-linear frictional moment model for incomplete spherical piston in spherical pump was derivated quantificationally. Parameter sensitivity analyses were conducted to find the low-friction structural pattern of the piston. The theoretical wear model of piston–cylinder pair is proposed as well.
Findings
To reduce the frictional moment between incomplete piston and cylinder, the optimised diameter ratio between piston pin and piston should be 0.12 based on the parameter sensitivity analyses. The maximum frictional moment is approximately 2.5 times of the minimum. The total efficiency should be considered synthetically based on the thickness of specific working medium.
Originality/value
The proposed non-linear frictional moment model offers the quantitative estimations. Parameter sensitivity analyses were conducted to find the low-friction structural pattern of the piston. The wear behaviours of the piston and cylinder were analysed to investigate the wear characteristics of the piston.
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The purpose of this paper is to study about tribological parameters of cylinder liner/piston ring under sliding contact in the presence of lubricant.
Abstract
Purpose
The purpose of this paper is to study about tribological parameters of cylinder liner/piston ring under sliding contact in the presence of lubricant.
Design/methodology/approach
A reciprocating test rig is used for the experimental work. The Taguchi approach has been adopted to optimize the coefficient of friction and minimum weight loss of piston ring and cylinder liner. Three control factors like load, speed and temperature were used for L9 orthogonal array design and ANOVA (analysis of variance). Parameters have been ranked on the basis of experimental outcomes and signal-to-noise (S/N) ratio analysis.
Findings
It is observed that coefficient of friction was greatly influenced by speed, and weight loss of piston ring and cylinder liner was greatly influenced by load. The surface morphology by SEM (scanning electron microscopy) analysis was used to understand the wear mechanism of worn-out surface and comparative evaluation was made with the Taguchi method.
Originality/value
Surface morphology of the worn-out surface is significantly dependent on the load condition which validates the ANOVA results.
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Qunsheng Wang, Bin Zhu, Fubin Zhang, Xuesong Jiang and Jie Wang
While the normal wheel–rail contact model cannot be accurately used for light rail transit (LRT) wheel wear analysis with large wheelset lateral displacement and wheelset yaw…
Abstract
Purpose
While the normal wheel–rail contact model cannot be accurately used for light rail transit (LRT) wheel wear analysis with large wheelset lateral displacement and wheelset yaw angle, a modified semi-Hertzian contact model (MSHM) is proposed in the paper.
Design/methodology/approach
MSHM was first proposed to consider the wheelset motion with the lateral displacement and the yaw angle. Then, a dynamic model of an LRT was established and the influence of some key factors on wheel wear is analyzed. At last, after operating for a certain mileage, the predicted wheel wear is compared with the tested wheel wear.
Findings
Compared with the tested wheel wear, the predicted wheel wear shows a good agreement with the measured result, verifying the accuracy of MSHM.
Originality/value
Considering larger wheelset lateral displacement and yaw angle, MSHM can be used to calculate the wheel wear of the LRT with high accuracy.
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The purpose of this paper is the more exact evaluation of distorted constriction contact resistance between two clamped slabs or thin films, having a bi-dimensional current lines…
Abstract
Purpose
The purpose of this paper is the more exact evaluation of distorted constriction contact resistance between two clamped slabs or thin films, having a bi-dimensional current lines structure.
Design/methodology/approach
Mathematical modeling using conformal mappings.
Findings
The influence of the tarnish film on the distorted constriction resistance is clarified and three new exact formulas are proposed for the distorted constriction resistance between clamped slabs with rectangular contact spot. Comparisons with early proposed formula for constriction resistance of slab narrowing and with finite element analysis results are presented.
Research limitations/implications
The research is limited to direct current and homogeneous and isotropic media and the results can be extended at alternate current when the skin effect is negligible.
Practical implications
Exact evaluation of 2D constriction contact resistance which appears in macro-scale contacts electrical equipment and in MEMS devices, particularly in crimp contacts.
Originality/value
The proposed formulas are new, original, simple and exact.
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This paper aims to propose a semi-analytical model to investigate the elastic-plastic contact between fractal rough surfaces. Parametric studies have been performed to analyze the…
Abstract
Purpose
This paper aims to propose a semi-analytical model to investigate the elastic-plastic contact between fractal rough surfaces. Parametric studies have been performed to analyze the dependencies between the contact properties and the scale-independent fractal parameters.
Design/methodology/approach
A modified two-variable Weierstrass-Mandelbrot function has been used to build the geometrical model of rough surfaces. The computation program was developed using software MATLAB R2015a. The results have been qualitatively validated by the existing theoretical and experimental results in the literature.
Findings
In most cases, a nonlinear relation between the load and the displacement of the rigid plane is found. Only under the condition of larger loads, an approximate linear relation can be seen for great D and small G values. (D: fractal dimension and G: fractal roughness).
Originality/value
The contact model of the cylindrical joints (conformal contact) with radial clearance is constructed by using the fractal theory and the Kogut-Etsion elastic-plastic contact model, which includes purely elastic, elastic-plastic and fully plastic contacts. The present method can generate a more reliable calculation result as compared with the Hertz contact model and a higher calculation efficiency as compared with the finite element method for the conformal contact problem.
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Deepak Kumar Prajapati, Jitendra Kumar Katiyar and Chander Prakash
This study aims to use a machine learning (ML) model for the prediction of traction coefficient and asperity load ratio for different surface topographies of non-conformal rough…
Abstract
Purpose
This study aims to use a machine learning (ML) model for the prediction of traction coefficient and asperity load ratio for different surface topographies of non-conformal rough contacts.
Design/methodology/approach
The input data set for the ML model is generated using a mixed-lubrication model. Surface topography parameters (skewness, kurtosis and pattern ratio), rolling speed and hardness are used as input features in the multi-layer perceptron (MLP) model. The hyperparameter tuning and fivefold cross-validation are also performed to minimize the overfitting.
Findings
From the results, it is shown that the MLP model shows excellent accuracy (R2 > 90%) on the test data set for making the prediction of mixed lubrication parameters. It is also observed that engineered rough surfaces with high negative skewness, low kurtosis and isotropic surface patterns exhibit a significant low traction coefficient. It is also concluded that the MLP model gives better accuracy in comparison to the random forest regression model based on the training and testing data sets.
Originality/value
Mixed lubrication parameters are predicted by developing a regression-based MLP model. The machine learning model is trained using several topography parameters, which are vital in the mixed-EHL regime because of the lack of regression-fit expressions in previous works. The accuracy of MLP with random forest models is also compared.
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Milan Omasta, Martin Ebner, Petr Šperka, Thomas Lohner, Ivan Krupka, Martin Hartl, Bernd-Robert Hoehn and Karsten Stahl
The purpose of this study is to investigate lubricant film-forming capability of oil-impregnated sintered material in highly loaded non-conformal contacts. This self-lubrication…
Abstract
Purpose
The purpose of this study is to investigate lubricant film-forming capability of oil-impregnated sintered material in highly loaded non-conformal contacts. This self-lubrication mechanism is well described in lightly loaded conformal contacts such as journal bearings; however, only a little has been published about the application to highly loaded contacts under elastohydrodynamic lubrication regime (EHL).
Design/methodology/approach
Thin film colorimetric interferometry is used to describe the effect of different operating conditions on lubricant film formation in line contacts.
Findings
Under fully flooded conditions, the effect of porous structure can be mainly traced back to the different elastic properties. When the contact is lubricated only by oil bleeding from the oil-impregnated sintered material, starvation is likely to occur. It is indicated that lubricant film thickness is mainly governed by oil bleeding capacity. The relationship between oil starvation parameters corresponds well with classic starved EHL theory.
Practical implications
To show practical, relevant limitations of the considered self-lubrication system, time tests were conducted. The findings indicate that EHL contact with oil-impregnated sintered material may provide about 40 per cent of fully flooded film thickness.
Originality/value
For the first time, the paper presents results on the EHL film-forming capability of oil-impregnated sintered material by measuring the lubricant film thickness directly. The present paper identifies the phenomena involved, which is necessary for the understanding of the behavior of this complex tribological system.
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